Hard disk drives include one or more rigid disks, which are coated with a magnetic recording medium in which data can be stored. Hard disk drives further include read and write heads for interacting with the data in the magnetic recording medium. The write head includes an inductive element for generating a magnetic field that aligns the magnetic moments of domains in the magnetic recording medium to represent bits of data.
Magnetic recording techniques include both longitudinal and perpendicular recording. Perpendicular magnetic recording (“PMR”) is a form of magnetic recording in which the magnetic moments representing bits of data are oriented perpendicularly to the surface of the magnetic recording medium, as opposed to longitudinally along a track thereof. PMR enjoys a number of advantages over longitudinal recording, such as significantly higher areal density recording capability.
Write poles with a trapezoidal cross-sectional shape at the air bearing surface (“ABS”) are used to provide improved writing performance in PMR heads. The manufacture of write poles with this trapezoidal cross-sectional shape presents a number of difficulties, however, not the least of which involve providing the pole with both desired side wall angles and desired track width, as these parameters are dependent upon one another in the manufacturing process. In this regard, in some manufacturing processes, attempting to achieve a specific side wall angle may result in an undesirable track width, and vice versa.
Moreover, when attempting to mill a write pole with a trapezoidal cross-sectional shape from a layer of magnetic material, manufacturing challenges can make it difficult to obtain a good trapezoidal shape. For example, as the magnetic material from which the write pole is milled may be deposited on a hard material such as alumina, the bottom of the pole (i.e., the trailing edge thereof) is often pinned during the final stage of the pole trim, rendering a sort of a “footing” feature which makes the pole profile appear to be pinched at a “waist” thereof. This effect is illustrated in FIG. 1, in which a scanning electron micrograph of a write pole is shown in cross-section. In the write pole of FIG. 1, a distinct “waist” and “footing” can be seen. To address this manufacturing limitation, some processes involve milling a write pole from a layer of magnetic material disposed over a non-magnetic buffer layer, whereby the footing is formed in the non-magnetic buffer, such that the portion of the structure comprising magnetic material approximates a trapezoidal shape. One such configuration is illustrated in FIG. 2. This approach suffers from notable drawbacks, such as pole protrusion, which can result when the non-magnetic buffer layer is heated during write operations and extends beyond the air bearing surface.